The invention relates to a multistage molecular evaporator with wiped off film with only one evaporating body with convex evaporating surface and with continuous redistillation. In the known apparatus for molecular distillation a number of devices are incorporated in such a way as to make possible a repeated distillation. This is a requirement because the separating ability of molecular evaporators is low for fundamental reasons as it represents approximately one theoretical evaporator plate. When a higher separation efficiency is needed or when a mechanical spouting of the distilled substance from the evaporating to the condensing surface occurs, repeated distillations have to be carried out either in one multistage device or in several apparatus connected to each other in a battery. Charging apparatus with numerous repeated distillations carried out in a cascade of distillation steps are described in the prior art as well as film apparatus with repeated distillation wherein liquid film is formed by the action of gravity or apparatus rotation (see our U.S. Pat. No. 4,053,006). A common drawback of these known distillation devices resides in that liquid mixing, respectively wiping off the running-down film is lacking, low evaporative capacity, low separating ability, long residing time and thermal decomposition are exhibited and, moreover, these known devices have complicated constructions. There is also known an apparatus with a centrifugal evaporating surface and with a divided condenser which is described in U.S. Pat. No. 2,234,166. This known apparatus is, however, from a constructional point of view, very complex and costly, and it has a low-effective heating of the high-speed rotating evaporating surface. Increased separating capability is primarily achieved by means of built-in materials and barriers mounted in the distillation space of molecular evaporators having means for wiping off film. In these known installations, the character of molecular distillation is nevertheless suppressed, or it is necessary to link a battery of a plurality of single evaporators in such a way that distillate from one evaporator is subjected to repeated distillation in other evaporators. The drawbacks of these known arrangements are as follows: they are complex to operate and require attendance by operating personnel; heated connecting members and intermediate pumping is needed, the contact time of the treated substance with heating surfaces is extended and due to the fact that a large number of packings and pumps are used, the danger of contamination with aerial oxygen increases. These drawbacks are partially eliminated in the continuous multistage molecular evaporator having only one evaporating body according to Czechoslovak invention No. AO 181054, and U.S. Pat. No. 4,053,006. This evaporator has several rotating liquid seals mounted in the space between the condensing and evaporating surfaces in a common evaporating body, which are conveniently mounted in such a way thay they mutually separate two adjoining vacuum stages. The rotating liquid seals are so constructed that they permit the passage of residues from the preceding vacuum stage into the next following vacuum stage as a feed. Redistillation cannot be, however, carried out in this multistage molecular evaporator with one evaporator body.